The present invention relates to systems and methods for the insertion of spinal fixation rods, or simply spinal rods or fixation rods, and in particular, to systems and methods for percutaneously guiding spinal fixation rods to a target location adjacent the spinal column.
Pedicle screw fixation systems have been in use for decades in order to fuse adjacent vertebral segments to improve spinal stability or correct certain spinal deformities. Older approaches for inserting these fixation systems involved open procedures, in which relatively large skin incisions were created to expose a substantial portion of the patient's spinal column, in order to allow for insertion of the pedicle screws and manipulation of spinal rods through openings in pedicle screws, such openings typically being in heads of the screws.
Over time, less invasive approaches have been developed. Typically, in such approaches, pedicle screws are inserted into the pedicles of selected vertebrae of a patient's spine through individual percutaneous incisions corresponding to the pedicle screws. Fixation or fusion rods are then inserted into the body through one of those incisions or through an additional incision adjacent to the most cephalad or caudal pedicle screw, and the rod is positioned through openings in the heads of the pedicle screws to fix the relative positions of the pedicle screws through which the rod is inserted. In some such minimally invasive procedures, a percutaneous access device (e.g., a cannula or portal) is connected to each of the pedicle screws and extends through the respective percutaneous incision. Such percutaneous access devices provide a pathway through the tissue from each incision to the respective pedicle screw, in order to aid in the insertion of a spinal rod. Examples of such percutaneous access devices are described in commonly-assigned U.S. Pat. No. 7,955,355 (“the '355 Patent”) and U.S. Pat. No. 8,002,798 (“the '798 Patent”), the entireties of which are hereby incorporated by reference herein as if fully set forth herein.
One example of a commercially used minimally invasive spinal fusion system is the MANTIS® Spinal System developed by Stryker Corporation, the assignee of the present application, and exemplified by the spinal fixation system shown in FIGS. 1A and 1B. As shown in those figures, blades 2 are connected to opposing sides of the heads 3 of pedicle screws implanted in respective vertebrae, such that the blades 2 extend posteriorly through respective incisions in the patient's skin and define pathways extending between each incision and the respective pedicle screw. In certain systems, the blades 2 may be separately formed from and detachably connectable to the pedicle screw heads 3, and, in other systems, the blades may be integrally formed with the pedicle screw heads 3 to form monolithic blade-screws. In the case of integrally formed blade-screws, the blades 2 may be connected to the pedicle screw heads 3 by frangible portions (e.g., reduced thickness portions, which may be defined by grooves formed in either or both of the interior and exterior surfaces of the blade-screws at the junction between the blades and the pedicle screw heads). Such frangible portions provide a location for the blades to be broken away from the pedicle screw heads when desired. With either form of the blades, a rigid ring 7 may be placed over and slid along each of the blades 2 until the rigid ring 7 abuts the skin of the patient. In this manner, the ring 7 may stabilize the spinal insertion system with respect to the skin and also provide rigidity to the spinal rod insertion system by maintaining the relative positioning of the blades 2 and resisting their disconnection from the pedicle screw heads 3. Similar blade and abutment ring structures are described in the '798 Patent.
In the minimally invasive approach illustrated in FIGS. 1A and 1B, a rod insertion tool 4 is used to insert a fixation rod 5 into the body between the blades 2, which act to provide percutaneous pathways and help to guide the movement of the rod 5 to the desired position connecting the pedicle screw heads 3. Following insertion of the rod 5, the blades 2 are intentionally disconnected from the pedicle screw heads 3 and removed from the patient.
When using a blade-screw having blades integrally formed with a pedicle screw head, one or both of the blades can be broken at the respective one or both of the frangible connections between the blades and the screw head during insertion and manipulation of the rod 5, and even during insertion of the blade-screw. In such instances, the broken blade-screw needs to be replaced in order to provide a guide in which to insert the fixation rod 5, requiring dilation to retract the blade-screw. Thus, there is a need for systems and methods to guide the fixation rod without dilation and without requiring the use of a separate guide.